Biological repair material compatible with biological tissue adhesive

ABSTRACT

An object of the present invention is to provide a means for improving the affinity of an in vivo embedded material such as an artificial blood vessel or an artificial dura mater with a tissue adhesive, so as to quickly prevent the leakage of the blood or spinal fluid. The present invention provides a polymeric material used in combination with a tissue adhesive, which comprises carbon or silicon as a constitutional element, and at least a portion of the surface of which is modified by ion bombardment.

TECHNICAL FIELD

The present invention relates to a repair material having an affinitywith a tissue adhesive, that is, a polymeric material that is used incombination with a tissue adhesive. More specifically, the presentinvention relates to a polymeric material that is used in combinationwith a tissue adhesive, at least a portion of the surface of which ismodified by ion bombardment, thereby resulting in an improved affinitywith the tissue adhesive, and a production method thereof.

BACKGROUND ART

Among three-layer membranes (pia mater, cranial arachnoid mater, andcranial dura mater) that are present in the cranial bone and protect thebrain parenchyma, the cranial dura mater is hardest and exists as theoutermost layer of the three aforementioned layers. Thus, the cranialdura mater is also considered to be the inner periosteum of the cranialbone. When neurosurgical operations are conducted, the cranial duramater must be excised in many cases, thereby resulting in the absence ofthe cranial dura mater. In addition, there may also be cases wherespontaneous contraction of the cranial dura mater per se makes theprimary suture difficult. If the operative site were sutured withoutclosing the cranial dura mater, it would cause serious complications.For example, it could cause a leakage of spinal fluid, which may resultin development of an intracranial infection, or it could cause theadhesion of the brain parenchyma to the bone or subcutaneous tissues,which may lead to local nervous symptoms or become a focal point of aseizure. Thus, when the operative site is sutured, a strict suture isrequired, so as to avoid the formation of gaps on the cranial duramater. Accordingly, in a case where a part of the cranial dura mater islost, or where the primary suture becomes difficult, it is necessary tocompletely suture the operative site using a certain supply material, soas to prevent the formation of gaps.

The type of a supply material that is used to compensate for the absenceof the cranial dura mater has been an important issue for a long periodof time, and has been discussed by neurosurgeons. Artificial materialswere initially used for a while, but they have been problematic in termsof biocompatibility, handlability, etc. Thus, such artificial materialswere soon abandoned. Auto fascia has most widely been used from theinitial stage to date. However, such auto fascia is also problematic inthat the original fascia is lost from the excised site, and that iteasily adheres to the brain. Dry human dura mater is a dura mater supplymaterial, which is produced by treating the dura mater collected fromthe dead body with radioactive rays. This material was the best amongthose that had ever been produced. However, the possibility emerged thatprions reportedly responsible for Creutzfeldt-Jakob disease exist in thedura mater. It was then reported that a patient became affected withCreutzfeldt-Jakob disease through the dry human dura mater. Inconsequence, the use of dry human dura mater was completely prohibitedin 1998.

At present, ePTFE (expanded polytetra-fluoroethylene) certified by theMinistry of Health, Labor and Welfare is the only material that can beused as a dura mater supply material other than the aforementioned autofascia. Since ePTFE is a polymeric material, it has no adhesiveproperties to living bodies. This is advantageous in that the materialdoes not adhere to the brain. On the other hand, since ePTFE has poorcontractility, the spinal fluid leaks through pin holes. Thus, it isnecessary to suture the operative site using a special surgical suture.Moreover, since ePTFE does not have adhesive properties to livingbodies, spinal fluid leakage occurs even from gaps on a sutured surface.Furthermore, since ePTFE does not have adhesive properties also toperipheral tissues, there is a high possibility that it functions onlyas a simple skeletal material. A large number of attempts have been madeto utilize such ePTFE to as great an extent. All of these attemptsrelate to a technique of using ePTFE as a skeletal material for thesubsequent formation of fibrous tissues around the ePTFE.

As a method of treating the surface of an artificial material with ions,a method involving plasma treatment has been known (Japanese PatentApplication No. 10-302170). This method comprises improving adhesiveproperties by modifying the surface of the material. A plasma-treatedlayer obtained by the plasma treatment method is unstable in livingbodies, and it has a risk of decomposing or peeling off over time. Inliving bodies, it is necessary to maintain a stable cell adhesion layerover a long period of time. When the aforementioned plasma treatmentmethod is particularly applied to the artificial dura mater, althoughthe material adheres to the contact surface of the cranial bone at theinitial stage, it has a risk of peeling off after a long period of time.

It has also been reported that the surface layer of an in vivo embeddedmaterial is modified using ions with higher energy than the ions used inthe plasma treatment, so as to enhance antibacterial properties(Japanese Patent Application No. 5-148994). The main purpose of thismethod is to reduce the infectivity of the embedded material.

DISCLOSURE OF THE INVENTION

In order to fix medical materials used in vivo for surgical operations,such as an artificial blood vessel, an artificial dura mater, or a patchmaterial for repairing the heart or blood vessels, to tissues for atherapeutic purpose, a method of fixing these materials to a living bodyvia anastomosis has been adopted. When such a medical material isanastomosed with a living body using a surgical suture, however, theblood or spinal fluid can leak from holes on the material through whichthe needle has passed. Accordingly, in general, such leakage isprevented by inducing blood coagulation by applying pressure on anaffected area, or by using a tissue adhesive known as fibrin glue.

It is an object of the present invention to provide a means forimproving the affinity of an in vivo embedded material such as anartificial blood vessel or an artificial dura mater with a tissueadhesive, so as to quickly prevent the leakage of the blood or spinalfluid.

As a result of intensive studies directed towards achieving theaforementioned object, the present inventors have found that ePTFE thathas been irradiated with an Ne ion beam has a higher affinity with atissue adhesive than that of unirradiated ePTFE, thereby completing thepresent invention.

Thus, the present invention provides a polymeric material used incombination with a tissue adhesive, which comprises carbon or silicon asa constitutional element, and at least a portion of the surface of whichis modified by ion bombardment.

The tissue adhesive is preferably fibrin glue.

The polymeric material comprising carbon or silicon as a constitutionalelement is preferably expanded polytetra-fluoroethylene (ePTFE),polylactic acid, or polyglactin.

The modification by ion bombardment is preferably carried out byirradiation with ions at a dose (φ) of 1×10¹²≦φ≦1×10¹⁶ ions/cm².

The polymeric material of the present invention is preferably used foran artificial dura mater, an artificial blood vessel, a patch used forthe heart or blood vessel, or a surgical suture.

In another aspect, the present invention provides a method for producinga polymeric material used in combination with a tissue adhesive, whichis characterized in that at least a portion of the surface of thepolymeric material comprising carbon or silicon as a constitutionalelement is irradiated with ions at a dose (φ) of 1×10¹²≦φ≦1×10¹⁶ions/cm².

In another aspect, the present invention provides a method for improvingthe affinity of a polymeric material comprising carbon or silicon as aconstitutional element with a tissue adhesive, which is characterized inthat at least a portion of the surface of the polymeric material isirradiated with ions at a dose (φ) of 1×10¹²≦φ≦1×10¹⁶ ions/cm².

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the interaction of unirradiated ePTFE with fibrin glue,which was observed 1 month after application of the unirradiated ePTFEto the rabbit. The unirradiated ePTFE did not adhere to fibrin glue.

FIG. 2 shows the interaction of ion beam-irradiated ePTFE with fibringlue, which was observed 1 month after application of the ionbeam-irradiated ePTFE to the rabbit. The ion beam-irradiated ePTFEadhered to fibrin glue via cells.

FIG. 3 shows a curve relating to an increased pressure in the brain ofthe rabbit, to which the ion-beam irradiated dura mater was applied.

FIG. 4 shows a device used for a pressure endurance test.

FIG. 5 shows the relationship among a leakage critical pressure, ionspecies, and a dose of radiation in a pressure test. 0 (zero) in legendsrepresents an unirradiated sample.

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiments of the present invention will be described in detailbelow.

The polymeric material of the present invention is used in combinationwith a tissue adhesive. The polymeric material of the present inventioncomprises carbon or silicon as a constitutional element, and it ischaracterized in that at least a portion of the surface thereof ismodified by ion bombardment.

In the present invention, a polymeric material comprising carbon orsilicon as a constitutional element is irradiated with an ion beam, soas to improve the affinity of the material with a tissue adhesive,thereby preventing the leakage of the blood or spinal fluid. The presentinvention also relates to a method for treating the surface layer of apolymeric material, which comprises irradiating the above-describedpolymeric material with an ion beam, so as to improve the affinity ofthe material with a tissue adhesive.

When the blood vessel injured due to abdominal aortic aneurysm or thelike is treated using an artificial blood vessel, the living bloodvessel is connected with the artificial blood vessel by suturing with asurgical suture. However, in the case of using an artificial bloodvessel made from a polyester or a fluorine compound, the blood leaksthrough pin holes, even using a surgical suture made from the samematerial.

Moreover, when a nidus is excised from the heart or blood vessel, theabsent portion should be repaired. In a case of seaming a repairmaterial with the blood vessel or heart also, the blood or tissue fluidleaks through pin holes. In the field of neurosurgery, when craniotomyis conducted to treat cerebral tumor, subarachnoid hemorrhage, a woundcaused by traffic accident, and so on, the cranial dura mater is lost.An artificial dura mater is used to compensate for such loss of thecranial dura mater. However, as in the case of the artificial bloodvessel, spinal fluid leaks through pin holes.

In many cases, a tissue adhesive known as fibrin glue is used to preventsuch leakage of the blood vessel or spinal fluid. Among materials usedfor artificial blood vessel or dura mater, fluorine compound materialshave extremely poor properties to adhere to fibrin glue, and thus, thesematerials are insufficient for preventing the leakage of the blood orspinal fluid.

In the present invention, the surface layers of these artificialmaterials are irradiated with an ion beam according to the ionimplantation method, so as to improve the adhesive properties of thematerials to fibrin glue. Such ion beam treatment can be carried out notonly on an artificial dura mater, an artificial blood vessel, or a patchused for the heart or blood vessel, but also on the surface layer of asurgical suture used for connecting these artificial materials withliving bodies. The adhesive properties of an artificial material tofibrin glue are improved by modifying the surface layer of a surgicalsuture with a beam.

A polymeric material used in the present invention, which comprisescarbon or silicon as a constitutional element, is not particularlylimited. Any material can be used, as long as it has biocompatibilityand handlability. For example, fluorocarbon resin molded products suchas expanded polytetra-fluoroethylene (ePTFE) or suicides such assilicone can be used. Polymeric materials preferably used in the presentinvention may include expanded polytetra-fluoroethylene (ePTFE) andbiodegradable polymers (e.g. polylactic acid, polyglactin, etc.). Ofthese, expanded polytetra-fluoroethylene (ePTFE) is particularlypreferable.

At least a portion of the surface of the polymeric material of thepresent invention is modified by ion bombardment. Examples of ionspecies to be implanted may include H⁺, He⁺, C⁺, N⁺, Ne⁺, Na⁺, N₂ ⁺, O₂⁺, Ar⁺, Kr⁺, and Xe⁺. However, examples are not limited thereto, unlesssuch ion species is eluted and inhibits the affinity of the polymericmaterial with a tissue adhesive. Preferred examples may include Ne⁺,Ar⁺, Kr⁺, and Xe⁺.

The dose φ (amount of irradiation) is preferably in a range of1×10¹²≦φ≦1×10¹⁶ ions/cm². If the dose is lower than 10¹² ions/cm², itseffect of significantly improving the affinity of the polymeric materialwith a tissue adhesive decreases. If the dose is higher than 10¹⁶ions/cm², the polymeric material is easily disrupted. Thus, both thecases are not preferable. The dose φ is more preferably in a range of1×10¹³≦φ≦1×10¹⁵ ions/cm².

With regard to ion acceleration energy, it is considered that energytransfer mechanism is varied depending on the level of such energy.Practically, the ion acceleration energy can be set within a rangebetween several tens of keV and several MeV. It is more preferably setbetween 50 keV and 2 MeV.

Beam current density is preferably set in a range that does not exceed0.5 μA/cm². This is because if such beam current density is too high,the temperature of the polymeric material as a target excessivelyincreases, and the polymeric material itself thereby degenerates, andalso because there is a risk that the affinity of the material with atissue adhesive decreases.

A means for giving ion bombardment in the present invention may be ionimplantation. Such ion implantation reaction is limited to aninteraction between an ion beam and a material to which ions areimplanted (target material). In addition, by selecting ion implantationenergy, ions can be embedded at any given depth from the surface. Thus,ion implantation is extremely excellent in controllability. This is acharacteristic that plasma treatment does not have. When ions areimplanted, electron stopping capability acts on ions with a relativelylow mass at the initial stage of diffusion, and nuclear stoppingcapability acts on ions with a relatively high mass from the initialstage. In spite of such a mechanical difference, the implanted ions heatthe polymeric material due to lattice vibration (thermal nonequilibriumstate), and cause dissolution, amorphization, and the like.

The polymeric material of the present invention is used in combinationwith a tissue adhesive. Preferred examples of a tissue adhesive mayinclude fibrin glue and a cyanoacrylate instant adhesive that is apolymeric adhesive. Conventionally, suture has been carried out with athread such as silk thread or catgut and a needle in surgicaloperations. For such suture, an adhesive has also been used. By theconventional suture methods, the suture of small blood vessels togetheror the repair of blood vessels have often been difficult. In addition,the conventional methods have also been problematic in that it generallytakes a considerable period of time for suturing and in that ugly scarremains after suturing. A tissue adhesive is adopted as a means forsolving such problems.

Fibrin glue is composed of fibrinogen freeze-dried powders, afibrinogen-dissolving solution, thrombin freeze-dried powders, and athrombin-dissolving solution. Fibrinogen freeze-dried powders aredissolved in a fibrinogen-dissolving solution, so as to obtain solutionA. Thrombin freeze-dried powders are dissolved in a thrombin-dissolvingsolution, so as to obtain solution B. The thus dissolved solutions arelaminated at equivalent volumes on an adhesive site. Otherwise, both thesolutions are mixed with each other at equivalent volumes, and themixture is applied thereto. Fibrin glue is a physiological tissueadhesive, which utilizes the final stage of blood coagulation.Fibrinogen contained in the fibrin glue becomes a soluble fibrin clot bythe action of thrombin. Then, the fibrin clot becomes a urea-insolublestable fibrin clot with physical strength by the action of the bloodclotting factor XIII activated with thrombin in the presence of calciumions. The thus obtained fibrin clot acts to adhere and close tissues.Fibroblasts grow in this stable fibrin clot, and collagen fibers orgranulation matrix components are generated. Thus, the tissues arerepaired, then reaching complete recovery. A specific example of suchfibrin glue may be Bolheal (product name) (Chemo-Sero-TherapeuticResearch Institute (Kaketsuken)).

Surgical treatments wherein fibrin glue is used for the purpose offixing living tissues may include occlusion of bleeding injuriesfixation of broken bones, anastomosis of peripheral nerves or smallblood vessels, reinforcement of tendon adhesion or tendon suture, andadhesion of parenchymal organs. Moreover, when an artificial productsuch as an artificial dura mater or artificial blood vessel isanastomosed with living tissues, fibrin glue is used to prevent thespinal fluid or blood from leaking through pin holes. Likewise, fibringlue is used together with a patch for repairing the absent portion ofthe heart or blood vessel, so as to prevent the blood from leakingthrough pin holes. In particular, ePTFE has been problematic in that ithas poor adhesive properties with fibrin glue. However, such a problemhas been solved by modifying at least a portion of the surface thereofby ion bombardment according to the present invention.

The present invention will be more specifically described in thefollowing examples. However, the examples are not intended to limit thescope of the present invention.

EXAMPLES (1) Ion Irradiation Treatment

A male Japanese white rabbit with a body weight of 2.5 to 3.0 kg wasused in the experiment. The scalp of the rabbit was excised in acoronary form under general anesthesia with pentobarbital, so that theskull was exposed. Expanded polytetra-ethylene (ePTFE) irradiated withan ion beam (Ne⁺, 150 keV, 5×10¹⁴ ions/cm²) using a 200 keV ionimplanter (Riken, Japan) was used as a sample. The periosteum coveringthe surface of the skull was completely removed, and the cranial bonewas then removed, so that the cranial dura mater was exposed.Thereafter, a hole with a diameter of several millimeters was made on aportion of the dura mater. The sample was placed on the dura mater, suchthat the non-irradiated face thereof was allowed to come into contactwith the dura mater, and thus that the ion beam-irradiated face thereofwas placed on the scalp side. Thereafter, a tissue adhesive (fibringlue; Bolheal (product name); Chemo-Sero-Therapeutic Research Institute(Kaketsuken)) was dropped on the ion beam-irradiated face and thenexcess solution was removed. The remaining tissue adhesive was allowedto fix with the remaining cranial bone. As a control, a non-irradiatedsample was also subjected to the same above operations. After droppingfibrin glue, the scalp was anastomosed with the skull, and the affectedarea was then covered.

(2) Observation (a) Observation by Naked Eyes

Several minutes after dropping of fibrin glue, the ion beam-irradiatedface favorably adhered to the peripheral bone tissues. In contrast, theadhesive force of the untreated expanded polytetra-fluoroethylene wasweak to such an extent that it moved by adding a weak force withtweezers.

(b) Observation by Histological Tissue Examination

On the second week after the sample had been embedded, the rabbit wassacrificed with Nembutal. Thereafter, the affected area was removedtogether with the peripheral tissues thereof in the form of a mass, andit was immobilized with 10% buffer formalin. On the ion beam non-treatedface, fibrin glue did not adhere to ePTFE at all. Thus, in order toavoid that the ePTFE was separated from the tissues, the sample wasexcised together with the peripheral tissues thereof. After the skullwas decalcified, the sample placed on the dura mater was embedded inparaffin. The sample was subjected to hematoxylin-eosin staining andMasson trichrome staining, and then observed with a microscope.

As a result, no adhesion was observed between the untreated ePTFE andfibrin glue on the second week (FIG. 1). On the other hand, the ionbeam-treated ePTFE adhered extremely favorably to fibrin glue (FIG. 2).

(3) Brain Pressure Addition Experiment

The scalp of a rabbit, to which the ion beam-irradiated sample wasembedded for 4 weeks under the same above conditions, was removed underanesthesia, and the portion in which the sample was embedded wasexposed. Thereafter, a hole with a diameter of approximately 1 mm wasmade on a cranial bone portion different from the above sample embeddedportion. A catheter for applying pressure to the brain was inserted intoone hole. Another catheter for measuring the brain pressure was insertedinto the other hole. The catheter was connected with a syringe pump, andthe brain pressure was increased. Thereafter, an artificial dura materand fibrin glue immobilizing the artificial dura mater were observed,and it was confirmed whether or not these materials were peeled off dueto the increased brain pressure. For pressurization, a 50-ml syringe wasconnected with a syringe pump, and a pressure was then applied at a rateof 1 ml/min. FIG. 3 shows the relationship between time and brainpressure. The brain pressure was approximately 10 mmHg before applyingthe pressure. 1.5 minutes after applying the pressure, the brainpressure began to increase. The brain pressure increased slowly at theinitial stage, but it increased drastically from 3 minutes after theapplication of the pressure. The brain pressure reached 70 mmHg.However, during such pressurization, the leakage of spinal fluid was notobserved from the ion beam-irradiated artificial dura mater that wasimmobilized with fibrin glue, and thus, it showed good sealingperformance.

(4) In Vitro Adhesive Force Evaluation Test

The adhesion of the ion beam-irradiated ePTFE with fibrin glue wasevaluated in vitro, using a pressure device.

In order to evaluate the adhesion, two ion beam-irradiated faces withthe same conditions were allowed to adhere to each other using fibringlue, and the adhesive force was measured. With regard to ion beamirradiation to ePTFE, He⁺, Ne⁺, Ar⁺, and Kr⁺ ions were irradiated at anacceleration energy of 150 keV at a dose of 1×10¹⁴, 5×10¹⁴, and 1×10¹⁵ions/cm². FIG. 4 shows a pressure resistance device.

In order to evaluate the adhesiveness of fibrin glue to unirradiatedePTFEs and ion beam-irradiated ePTFEs, a sample that was cut into around form with a diameter of 15 mm was connected with a square samplehaving a round hole with a diameter of 10 mm such that both non ionirradiated faces or both ion beam irradiated faces were adhere to eachother using fibrin glue. A fibrinogen solution was applied around poreC, a thrombin solution was added dropwise thereto, and B was placed onit. While mixing the two solutions, B was allowed to closely come intocontact with C. The contacted portion corresponds to the overlappedportion between the circle with a diameter of 15 mm and the circle witha diameter of 10 mm, which was fixed with fibrin glue.

ePTFE (B+C) fixed with fibrin glue was immobilized on the upper portionof an acryl cylinder (D). 30 minutes later, the fixed portion B+C wasplaced on the cylinder D, which was filled with water stained with ink.An acryl plate A having a hole with an inner diameter of 17 mm wasfurther placed thereon, and the pressure was applied thereto, so thatthe device was immobilized.

Under these conditions, water was injected from a pressure-applying portF into the cylinder D at a rate of 60 ml/h. During this operation, thepressure in the cylinder D was measured using a pressure sensor via amonitoring port E, until water leaked from the contacted portion of Band C.

FIG. 5 shows the relationship among a leakage critical pressure, ionspecies, and a dose of radiation in a pressure test. Water leaked fromthe contacted portion of two unirradiated ePTFE faces by applying apressure of approximately 20 mmHg. In contrast, in the case of theadhesion of two ion beam-irradiated ePTFE faces, the withstandingpressure significantly increased. In particular, the critical pressureincreased to 100 mmHg, when a sample irradiated with an Ar⁺ ion beam ata dose of 1×10¹⁴ ions/cm² was used. Thus, it showed favorable adhesiveproperties.

INDUSTRIAL APPLICABILITY

The present invention enables the improvement of the affinity of amaterial that is embedded in a living body, such as an artificial bloodvessel or an artificial dura mater, with a tissue adhesive. When thepolymeric material of the present invention is used as a materialembedded in a living body, such as an artificial blood vessel or anartificial dura mater, it can prevent the leakage of the blood or spinalfluid.

1. A method for improving affinity with a fibrin glue of a polymeric material comprising carbon or silicon as a constitutional element, the polymeric material comprising expanded polytetra-fluoroethylene or silicone, comprising irradiating at least a portion of a surface of the expanded polytetra-fluoroethylene or silicone with ions at a dose (φ) of 1×10¹²≦φ≦1×10¹⁶ ions/cm² to form an ion-modified expanded polytetra-fluoroethylene or silicone; and applying the fibrin glue to the irradiated at least a portion of a surface of the expanded polytetra-fluoroethylene or silicone, wherein the ion is He⁺, Ne⁺, Ar⁺, or Kr⁺.
 2. The method according to claim 1 wherein the ion-modified expanded polytetra-fluoroethylene or silicone includes a non-irradiated portion and the non-irradiated surface is placed into contact with dura mater.
 3. The method according to claim 1 wherein the expanded polytetra-fluoroethylene or silicone is an artificial dura mater, an artificial blood vessel, a patch for the heart or blood vessel, or a surgical suture.
 4. The method according to claim 1 wherein the expanded polytetra-fluoroethylene or silicone comprises expanded polytetra-fluoroethylene.
 5. The method according to claim 1 wherein the expanded polytetra-fluoroethylene or silicone is an artificial dura mater.
 6. The method according to claim 1 wherein the irradiating at least a portion of a surface of the expanded polytetra-fluoroethylene or silicone comprises irradiating with ions at a dose (φ) of 1×10¹³≦φ≦1×10¹⁵ ions/cm².
 7. The method according to claim 1 wherein the expanded polytetra-fluoroethylene or silicone comprises silicone.
 8. The method according to claim 2 wherein the expanded polytetra-fluoroethylene or silicone comprises expanded polytetra-fluoroethylene.
 9. The method according to claim 2 wherein the expanded polytetra-fluoroethylene or silicone comprises silicone.
 10. The method according to claim 3 wherein the expanded polytetra-fluoroethylene or silicone comprises expanded polytetra-fluoroethylene.
 11. The method according to claim 3 wherein the expanded polytetra-fluoroethylene or silicone comprises silicone.
 12. The method according to claim 5 wherein the expanded polytetra-fluoroethylene or silicone comprises expanded polytetra-fluoroethylene.
 13. The method according to claim 5 wherein the expanded polytetra-fluoroethylene or silicone comprises silicone.
 14. The method according to claim 6 wherein the expanded polytetra-fluoroethylene or silicone comprises expanded polytetra-fluoroethylene.
 15. The method according to claim 6 wherein the expanded polytetra-fluoroethylene or silicone comprises silicone. 